Recently, there has been increased a demand for experiments of detecting oxygen (O2) gas molecules and nitrogen monoxide (NO) gas molecules under biological conditions by using an electrochemical sensor. This is because oxygen gas molecules and nitrogen monoxide gas molecules act an important role as signaling molecules in vivo. Oxygen is essential to keep most living organisms alive, and nitrogen monoxide is important for biological and physiological processes such as vasodilatation and neurotransmission. The oxygen and the nitrogen monoxide closely interact with each other in vivo. By way of example, when temporary hypoxia occurs, the nitrogen monoxide acts as a signaling molecule for inducing vasodilatation, so that a sufficient amount of oxygen is supplied to solve the hypoxia.
Various methods have been used to effectively detect nitrogen monoxide and oxygen. However, particularly, a nitrogen monoxide gas has a short lifespan in a radical state and a very small amount of the nitrogen monoxide gas in a nanomolar concentration can be present in vivo, and, thus, the nitrogen monoxide gas is difficult to detect. Typically, a chemiluminescence method or electron paramagnetic resonance spectroscopy has been used as a method for detecting nitrogen monoxide. These methods are used to analyze a material produced as a result of a reaction between nitrogen monoxide and other materials. However, these methods require relatively complicated analysis and high cost, and, thus, it is difficult to apply these methods to real-time analysis in a biological system. Meanwhile, an electrochemical sensor immediately responds to a gas, and, thus, it can detect a gas before the gas disperses and disappears, and it is suitable for real-time analysis. However, there are many kinds of electrochemical sensors and capacity of a sensor is affected by a kind of a compound contained in an electrode of the sensor. Therefore, a study for developing a high-capacity electrochemical sensor is still needed.
In a sensor including an ultra microelectrode having a diameter on a micrometer or nanometer scale, a voltage drop phenomenon and a double-layer charging effect can be reduced and a material can be delivered to a surface of the electrode at high speed. Therefore, there have been many attempts to install an ultra microelectrode in a sensor to detect, in real-time, a concentration of a gas at each local position in the vicinity of a gas generation source.
By way of example, Korean Patent Application No. 10-2008-7027651 entitled “Nanopore particle analyzer, method of preparation and use thereof” describes a nanopore electrode as one of ultra microelectrodes. However, there is lack of research for maximizing an ability of a sensor for selectively sensing a gas by simultaneously controlling a kind of a compound contained in an electrode of the sensor and morphology of the electrode.